LEILA signalling frequency choice question

  • While making adjustments to my station I must admit being guilty to triggering LEILA (I'm sorry, guys!).

    But, I found that I didn't hear LEILA, I only saw LEILA on monitoring. So I investigated closer.

    When sending a carrier, my radio sends a carrier on "carrier frequency" of the USB signal. Using USB means that the modulation will be above the carrier frequency.

    When LEILA triggered, I found it sends a carrier on the frequency it "discovered" and a lower frequency. That means the LEILA signal will be outside my filter, which explains why I didn't hear it.

    My question: why does LEILA use the "discover frequency" and a lower frequency for signalling instead of using a higher frequency so it would be in the passband of my receiver?